<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <style>
    * {
      margin: 0;
      padding: 0;
    }
    html {
      font-size: 100px;
    }
    @media screen and (min-width: 320px) {
      html {
        font-size: 50px;
      }
    }
    @media screen and (min-width: 640px) {
      html {
        font-size: 100px;
      }
    }

    .top {
      height: 1rem;
      font-size: 0.5rem;
      background-color: green;
      color: #fff;
      text-align: center;
      line-height: 1rem;
    }
  </style>
  <body>
    <div class="top">购物车</div>
  </body>
</html>
